Gravitational effects are important on stellar scales; it might also be
possible to mimic such effects in laboratory Bose-Einstein
condensates [1]} and thus emulate gravitationally bound, condensed,
assemblies of bosons, which are candidates for dark-matter
halos [2]}, [3]}, [4]}, [5]}. Although
many experiments have been carried out to establish the identity of dark
matter, there is still no unambiguous dark-matter candidate. For many years the
front runners have been weakly interacting massive particles (WIMPs); but their
existence has not been established convincingly (see, e.g.,
 [6]}, [7]} and references therein), so
investigations of other candidates, e.g., axions, boson stars, black holes, and
superfluids, have experienced a
renaissance [8]}, [9]}, [10]}, [11]}, [12]}, [13]}, [14]}.
